Multiple flour bleaching process



Filed Aug; 16;' 1940 NBN@ .BONE S Patented July 13, 1943 MULTIPLE FLoUR BLEACHING PROCESS Charles G. Ferrari, Minneapolis, and Willis S2. Hutchinson, St. Paul, Minn., assignors to General Mills, Inc., a corporation of Delaware Application August 16, 1940, Serial No. 352,910

4 Claims.

The present invention relates tu the improvement of wheat flour and other edible finely divided milled products, including the color, baking, and keeping qualities thereof and more particularly has reference to processes for the bleaching and ageing or maturing of flour and the like.

The principal object of our invention is tov provide a, process for the production of a bleached flour of excellent color without either adversely affecting its baking properties or its keeping qualities.

.will enable baked goods of greater volume to be produced from the iiour bleached by our process than would be produced from flour bleached by conventional bleaching methods.

A still further object of our invention is to provide a process for the multiple bleaching and maturing of wheat our and other edible finely divided milled products which comprises exposing ilour or other iinely divided products While agitated in a finely divided state to the action of a gaseous bleaching agent for a sufficient length of time and at a sucient partialpressure of the gas to at least partially bleach the flour or other nely divided product and then exposing the flour or other iinely divided product while agitated in a finely divided state to the action of a second gaseous bleaching agent of a similar or different nature than vthat used in the, ilrst bleaching operation, for a sumcient length of time and at a sulcient partial pressure of the gas to completely bleach and mature the flour or other edible finely divided product.

These and other objects, as will hereinafter appear, are accomplished by this invention which may be practiced in appaatus shown in the accompanying drawing in which Figure 1 is a vertical section through a double compartment agitator with suitable seals for the gas; and

Fig. 2is a transverse section on the line 2--2 of Fig. y1.

The foregoing gures illustrate a type of apparatus for carrying out the present invention. It consists essentially lof an agitator having a housing I with a central horizontal partitionV II dividing the agitator intoupper and lower compartm'gnts I2 and I3, respectively. Upper and afts I 4 and I5 are journalled in suitable sjgcarried by the partition housing, the en bymeans of a belt I6 and a pulley I1. This shaft in turn has a pulley I8 which drives a pulley I9 on the shaft I4 by means of a belt 20.

The shaft I4 carries a series of paddles 24 which serve to beat the iiour ,and to help keep it in suspension in the air of the upper compartment. This shaft also carries a series of propeller blades which cause the flour on the partition I I to be moved from left to right as will presently be more fully explained;

Similarly, the shaft I5 is provided with paddles 26 and with propeller blades 21, the latter, however, being set rcversely to the blades 25 so as to propel the flour resting on the bottom IIa from right to left.

Flour is fed to the agitator by means of a chute which is provided with a flour seal 3| to prevent gas within the compartment I2 from passingup through this chute. Thus ilour is delivered to the agitator at the left-hand end of the shaft I4 and is propelled to the right.

The diluted gas for bleaching in the compartment I2 lis supplied thereto through a pipe/35 and may be mixed with several times its volume of air in a mixing valve 36 which may be of any suitable type for this purpose. Gas is fed to the compartment I3 through a pipe 4D and may be mixed with a suitable amount of air by means of a mixing valve 4I.

The compartments I2 and I3 are separated by means of a suitable our seal 42 which maintains at all times a suitable depth of our at this point so that gas from one compartment will not readily pass to the other. Likewise, a flour seal 43 is provided at the outlet end of the comparty ment I3 to prevent gas therein from passing to the delivery chute 44 by means of which the bleached flour leaves the agitator.

.It will be seen from the foregoing that flour to be bleached passes down through the chute 30 into compartment I2 where it is violently agitated and mixed with the flrst bleaching gas and is propelled toward the outlet end at the right by means of the propeller blades 25. As the iiour which has thus passed its rst bleaching operation passes the ilour seal 42 it is picked up by the propeller blades 21 on the shaft I5 and moved to .the left. At the same time, the paddles 26 cause it to be violently agitated so as to bring it intimately into contact with the second bleaching gas in the compartment I3. As it passes from edible finely divided product.

According to present commercial bleaching processes, ilours are bleached and aged in separate stages of treatment. For example, the initial treatment is accomplished with' gaseous nitrogen trichloride which matures the our. Ni-

trogen trichloride, in addition to being a maturing agent, also possesses bleaching properties, but when used in suilicientz amount to obtain a complete comercial color removal, injuries the Therefore, for this reason, `nitrogen trichloride is used in an amount not quality of the iiour.

substantially in excess of that required to mature or age the flour, and the necessary additional bleaching is accomplished by a subsequent treatment with benzoyl peroxide, which has no maturing properties. The process outlined above is Atime-consuming since benzoyl peroxide is a solid which comprises exposing the iiour or other edible finely divided milled products, while agitated in a finely divided state, to the action of a gaseous bleaching agent for a sufiicientlength of time and at a sumcient partial pressure of the gas to at least partially bleach the flour or other flnely divided product and then exposing the ilour or other iinely divided product, while agitated in a iinely divided state, to the action ofv a second The present bleaching procedures generally used in industry are based almost entirely upon trial and error experiment. 'I'his ispartly caused by the fact that the mechanism of bleaching and treating flour by so-called bleaching agents is not fully understood. It is further caused by the fact that experiments necessary for any thorough investigation are comparatively expensive. Any such study is complicated by the differences that exist between various types of wheat during the same season and between the same types of wheat-l from different crops.

In commercial use today there are three types of bleaching reagents: gaseous, liquid and solid. The solid reagents are represented mainly by benzoyl peroxide. The most important gaseous reagents' at present are nitrogen peroxide, NO2, N204 nitrogen trichloride, NCI: and chlorine. Various other reagents which have been used occasionally or have been suggested are, for example, as follows: nitrosyl chloride and hydrogen peroxide aswell as various liquid fatty acid peroxides. Gaseous reagents react practically instantaneously with the flour, whereas the solid gaseous bleaching agent ofa similar or different l nature than that used in the first bleaching operation, for a sumcient length of time and at a sufficient partial pressure of the gas to complete the bleaching and maturing of the flour or other As an alternative to the process set forth above, we may mix or blend a stream of flour which has been so treated with another stream of ilour which has also been 'similarly treated with other gaseous reagents thereby producing a flour having the desired color, keeping qualities, and baking properties. j

The term "multiple bleaching as used in the specification and claims refers to a method of applying gaseous bleaching agents. In multiple bleaching, flour is treated'with multiple doses of bleaching reagent. Two variations occur when the repeated doses consist on the one hand of the same bleaching reagent and on the other hand of different reagents. We have found that both variations give improved results.

The use of so-called bleaching agents on flour has two basic objectives: (1) To improve the color of the iiour; and

(2) To improve the baking properties of the our.

l The Vbest result would be a combination or the two. Y In making the above statement, it is understood that the problem of bleaching varies from reagents' act slowly and may require as much as 10 to 20 hours to cause substantially all the color removal of which they are capable after complete blending has taken place. 'I'he present invention is concerned solely with the fast-acting reagents, that is, with the gaseous classification.

As heretofore stated, `partial or total elimination of benzoyl peroxide is a desired objective because the cost of that material is very high, that is, at present about one dollar per pound for a commercial product. containing about 16% of the active agent, benzoyl-peroxide, or from one cent to three cents per barrel of finished flour, when one iiour to' another and that in many cases the desired ,objective would beto improve the color of the our without injuring its baking properties. These objectives have been soughtvfor a number of years in all branches of the milling industry. ,Various bleaching reagents have been brought out from time to time and'have been adopted or discarded depending upon their merits and the cost thereof. The general objective of the present invention Vwas to obtain the above improvements in greater degree and at lower costs.

.suitable single compartment agitator.

used in combination with gaseous reagents.

According to the prior art, the desired amount of reagents was determined on a small scale.I

This quantity was then added to the flour in a The gas usually consisted of a single component, for instance, chlorine.

According to the present'process, the gases' used in bleaching are applied only in comparatively small quantities and have been diluted with air to low partial pressures, say in the order l of 0.5 to 35 mm. of mercury.

For convenience in reference, the vbleaching agents herein mentioned are listed showi'ng both the chemical name and formula. All but #6 are gaseous.

Reagents considered Chemical name Formula How produced l Nitrogen peroxide.-. N02,N204 Generated by passage arc.

May be produced aci cordingto the process set forth in U. S. Pat. No. 2,172,434, dated Sept. 12, George L. Cunning- 2 Chlorine dioxide.-.. ClOr ham. Reactiolk of chlorine with a' soluble ammonium salt. Electrolysis of salt solu-v tion. l

iTreating chlorine water with limestone. (C|H|CO)203 3 `Nitrogen trichloride.

4.A Chlorine-;

Hypochlorous acid.. l

Reaction between benzoyl chloride and a suitable peroxide.

6 Benzoyl peroxide...

Rleagents numbered 1 3, 4 and 6 are now in widespreadcommercial use. l

of air overelectric The ultimate results of bleaching processes must be interpreted in the light of both the color of the our and the quality of the finished product. Both factors are important although the latter may be considered the ultimate' test. Nevertheless, color removal may be taken as a denite index of the bleaching efliciency of the new processes for bleaching which are described herein. This is true because a numerical value can be given to the our color by measuring the carotenoid pigment content by suitable means. Flour color is conveniently expressed as parts of carotene per million parts of flour. Therefore, a high carotene value means a large amount of yellow color in the flour, while a low carotene value means a greater part of the color has been removed. Flour bleached according to our process has a very superior white -color which indicates a carotene content of approximately A to 1.1 parts per million parts of flour, depending on the initial carotene content of the flour. This carotene content is determined by the naphthaalcohol procedure.

M altiple treatment of flour with the same bleaching gas Applicants research in the field of flour bleaching led them to believe that there was ineicient utilization of a gaseous bleaching reagent when it was added to the iiour, and a series of experiments were made to demonstrate this fact and to indicate a more efficient procedure. For example, laboratory tests according to the prior art might indicate on a given flour that four grams of nitrogen trichloride per barrel of iiour were needed to obtain a suitable bleach. It is customary to express dosages of bleaching re- .agents in terms of grams or ounces per barrel each of nitrogen trichloride per barrel of flour accomplished the same result that a single dose of four grams of nitrogen i :ichloride per barrel of flour would give in terms of color removal. At other times, two successive doses of approximately 1.5 grams each would give the same result. This is of considerable importance because the cost of total reagent used is materially decreased, but it 4may be even more important because of the possibility of achieving a very interesting and valuable additional result. It is possible to overtreat a flour with a bleaching reagent, both from the standpoint of color, baking properties, and keeping qualities.Y With the usual methods of applying bleaching agents, adequate color removal may be accomplished but with certain types of flours this result cannot be accomplished without sacriiicing desirable baking properties and keeping qualities. Therefore, the application of repeated small dosages, which achieve adequate color removal with a lower total dosage of bleaching reagent and which may not have a deleterious eiect on the baking properties may be a decidedly advantageous way of applying the bleaching reagent.

Multiple bleaching with dissimilar gases This phase of applicants invention will be prefaced by the following example of the procedure used.

Bakers patent flour is fed into an agitator (as shown in the drawing) at the rate of twenty barrels per hour. In the conventional equipment, the flour enters at one end of the agitator and is gradually moved to the other end as a result of the action of a series of agitating blades Awhich keep the our in constant motion and keep a part of it in suspension in the free space above the body of the our. This iiour after the bleaching treatment exits at the opposite end of the agitator. Nitrogentrichloride (in this example, a total of two grams per barrel), is introduced into the agitator at 1ow-partial pressure at the same end at which the our enters. This partial pressure is adjusted to the optimum level for the efficient utilization of the chemical bleaching agent by varying the speed ofA the our through the agitator or by varying the amount of air which is introduced into the agitator. In our experiments, the reaction between the gaseous bleaching agent and the iiourl in the rst bleaching compartment is complete but the iiour, from the rst compartment, has not been bleached to the desired level, as this completion of the bleaching and maturing of the Bour occurs in the secondl bleachingl compartment of the agitator after the exposure of the iiour, in a" finely divided condition, to the action of the second bleaching gas. 0n leaving the iirst agitator the flour passes to the second bleaching compartment of the agitator through which it again travels in the manner described above. However, nitrogen peroxide is added to the second, bleaching 'compartment of the agitator at the rate of approximately 11/2 grams per barrel. In this operation, the gases are metered by commercially available equipment and the individual operations are carried out according to normal bleaching procedure.

The partial pressure of the nitrogen trichloride in this example, howevenwas about one millimeter of mercury and the partial pressure of nitrogen peroxide was approximately 2 mm. of Hg.

A similar bleaching run was made applying the same quantities of gas in the reverse order. I'he results of this series of experiments which are illustrative of our process are given in the following table:

Bleaching-7v action of dierent methods of applica- Comparison of the last two results illustrated above, shows that the order of application is important. that is, nitrogen trichloride followed by nitrogen peroxide, is the preferred 4method for bleaching action, from the color removal standpoint.

Some reagents are more efficient in removing color (carotenoid pigments principally)v than others. Nitrogen peroxide in this respect is regarded as a weak reagent andv is not used ac-- cording to present bleaching practice as the sole The order listed in the last example,`

color removing agent, because adequate color removal is not achieved. Color removal experiments have demonstrated that not all color is removed with equal facility. Thus the initial bleaching action seems to take place most readily. After each increment of color removal, the residual color has been more difficult to remove with the same reagent. In other words, it requires relatively more reagent to achieve the last fraction of color removal than the first. On this basis, when two reagents like nitrogen trichloride and nitrogen peroxide are applied, the former being a much stronger color removing agent than the latter, it would seem that the weaker reagent nitrogen peroxide should be used first to remove the more easily bleached portion of color. In our experiments, the surprising result was that this was not true, and we have demonstrated that the reverse order is preferable, namely, nitrogen trichloride followed by nitrogen peroxide.

Similar experiments made with -combinations of the common gases already listed show that in vmost cases there is a preferential order of application for the attainment of optimum bleaching action. The order of preference for the gases tested depending upon the desired result to be attained is shown in the following table,

' but since the mechanism of bleaching is not fully known, and since only a few reagents are available, no general pattern can be given but instead a preferred order for each pair of reagents has been indicated:

Preferentz'al order of application and bleaching action First gas: Second gas: NCla +flour NOx-l-same flour C12 -l-flour-)NCla-l-same flour C12 +our ClOz+same flour C102 +flour NClslsame fiour HOCl-l-flour-ClOz-i-same flour 'I'he above table indicates the preferred order of application for maximum color removal andis frequently the order for optimum maturing action. However, the reverse of the order indicated above is sometimes preferable when ptimum baking properties alone are considered. For example, with some fiours it has been found that nitrogen peroxide followed by nitrogen trichloride resulted in optimum baking properties, but not maximum color removal.

Our researches did not indicate that there is any preference in,VA order for hypochlorous acid versus chlorine or for hypoehlorous acid versus.

nitrogen trichloride.

As applied to the bleaching reagents listed in this table', it is possible to place them in such Y an order that the best results are obtained when any one of the gases listed is followed by any one of the reagents listed below it. Such an order with the exceptions noted above is as follows:

Cl Chlorine HOC1 Hypochlorous acid C102 Chlorine dioxide NCI; Nitrogen trichloride NO2 Nitrogen peroxide '.I'he value of applicants processes of multiple bleaching Ihas been stated to a certain extent, but there are other valuable results which also appear. Normally, one gaseous reagent was used as far as it was considered safe without injuring baking properties and then Novadel (benzoyl. peroxide) was added to the our to give the rest of the bleach. The amount of benzoyl peroxide used was held to a minimum because of its high cost. If nitrogen trichloride is used in too great a quantity, the flour is injured, and one or more of the baking characteristics of Vthe our are not satisfactory. Therefore, the amount that can be used is limited and the cost for benzoyl peroxide increases.

Nitrogen peroxide is very inexpensive because it is easily generated by the electric arc. However, when it is added alone in amounts large enough to produce adequate color removal, there is a definite tendency for the flour to become rancid.

For these reasons nitrogen peroxide is used commercially for only a part of the color removal and is followed usually by benzoyl peroxide to complete the desired color removal.

It vhas been found experimentally that little or nothing is gained by mixing nitrogen trichloride and nitrogen peroxide simultaneously in the same agitator. Thus, for exampleI two grams of nitrogen trichloride applied to a ilour gave a resultant carotene value of 1.22 P. P. M. When two grams of nitrogen trichloride and 0.75 gram nitrogen peroxide were added simultaneously to the flour the carotene value was likewise 1.22 P. P. M. Thus, the addition of nitrogen peroxide was of no value and did not lead to more color removal. It was discovered by experiment that` some unexpected and valuable results are obtained by selecting a preferred order of treatment, namely, when nitrogen trichloride treatment is followed by nitrogen peroxide treatment. -A greater color remoV/al is achieved and improved baking properties result, as will be seen by the following example:

Further, it has been found that considerable advantage accrues when a gaseous bleaching agent is added in small increments instead of as a single dosage. When the sum of the increments equal the quantity of reagent used in a single treatment substantially more color removal is accomplished by the former than the latter, and this may beA the desired result. On the other hand, less and sometimes considerably less bleaching reagent may bev added in small increments with the same bleaching effect the larger single treatment had, a result that is frequently advantageous. The advantage resides in the circumstance that bleaching sometimes injures the baking properties of the flour and hence the smaller the dosage of reagent required for ade- -quate color removal the better, in fact, adequate color` 'removal may be achieved without causing substantial damage to baking properties. In general, these results will be to bleach flour more cheaply and in many cases to improve baking qualities with benefit to the miller, the baker and the ultimate consumer.

Multiple bleaching followed by blending In addition to the procedure outlined above, a stream of our may be bleached by the successive action of two similar gases or'by the successive action of two dissimilar gases and then this flour stream may be blended with another portion of flour which has been treated by the successive action of two bleaching agents to obtain desirable results. This makes it possible to obtain optimum balance between bleaching action and change in the baking properties. It is obvious that certain combinations oi iiour may be better for general use than either one of the ours alone, but in order to get an effect that is of commercial value, it is necessary to increase the benets by considerable' amounts, The results oi such a test are given Hin the following table which shows the scoring of bread baked from iour prepared by various treatments of the same lot of patent our:

v volum Carotene Treatment per barrel Crumb Crumb 01H10 content of ilour color grain oi treated iiour 1 Control test-2% 10 10 2,800 0.80

grams o! nitrogen trichloride+0.032 oz. benzoyl peroxe. 2 1.75 oz. chlorine, iol- 10, dull 10 2, 670 0.87 lowedbyigmaNOg. white 3 3 grams nitrogen tril0, dull 10 2,655 0.78

chloride, followed creamy. l 1 by 1.5 grams N01. K 4 Blend 50%, #2, 50% i3. ll 10+ 2,795 0.83

From the above table it will be noted that the volume oi the bread baked with the blend of #2 and #3 isjust as good as that of bread baked with the control :Hour in spite of., the fact that bread baked with either of the component parts of the blend showed a very marked decrease in the size of the loaf. In addition,`v the combination of these two ours yields a iinal loaf which has a measurably improved crumb color and grain. Such results could not have been predictedy but evidently must be attributed to a complementary action of the treatments on the our. It lwill be ynoted that the crumb color is graded in units. The crumb color oi' a selected standard loaf is taken as 10.- The higher number indicates a better color; the rating of 11 ismeasurably better than 10; When applied to some other iloursot varying grade, the results sometimes are even greater. In this example, the treatment consisted of dividing a given flour into two parts. treatingl each ,part with two diierent gases in succession and then combining the parts after treatment. Another method of utilizing this same principle is to treat two or more separate ours with a suitable succession of bleaching agents and then blend the treated flour; or to treat various groups of hour streams from the same wheat Arrrix with the same or diiierent types of treat` ents and then to combine these streams to form l For. example, threesimpleclassiiications of iiour v 4ar asfollowsz. (1) Bread flour; (2) Cake hour;

( All-purpose or family hour.

While the present invention has been described with particular reference to the treatment of Y wheat hour. it will be apparent that the inven-A tion is not limited thereto but may also be ap- -plied to various other, streams of milled prodterm means in commercial milling, namely color removal with or without accompanying improvement inthe baking properties.

While the invention has been described in detail with specic examples, such examples are illustrative and are not given as limitations, since other modifications within the spirit and scope of the invention will be apparent to those skilled in the art.

We claim as our invention:

1. A process of bleaching iiour products and other nely divided milled cereal products which comprises contacting said product, Whileagtated in a inely divided state, with a gaseous bleaching agent for a time suiiicient to bleach said product partially, and then contacting the thus partly bleached product, while agitated in a finely divided state, with a further quantity of said gaseous bleaching agent for a time suilcient to vbleach said product further.

2. A process of bleaching iiour products and other nely divided milled cereal products which comprises contacting said product, while *agi* tated in a finely divided state, with a gaseous bleaching agent included in the following list:

Chlorine' Hypochlorous acid Chlorine dioxide l Nitrogen trichloride for a time s'ufdcient to bleach' said product partially, and then contacting the thus partly treated product, while agitated in ailnely di- Avided state, with a gaseous bleaching agent inand then contacting the thus partly treated prodother iinely divided 'milled cereal products which uct with nitrogen trichloride to bleach said product further.

4. A process o i' bleaching flour products and comprises contactingsaid product, while agitated in a finely divided state, with a gaseous bleaching agent for a time sumcient to bleach said product partially, thereafter contacting the thus partly bleached product, while agitated in a fineLv' divided state, with a. gaseous bleaching agent for a time sumcient to bleach said product further, and blending said product with another ilnely'divided milled cereal product treatedin the same manner by a ous agents.

CHARLES G. FERRARI.

WILLIS B. HUTCHINBON. ,l

diierent combination of gase- 

